1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium, and a magnetic recording/reproducing apparatus.
2. Description of the Related Art
Recording density of a hard disk drive (HDD), which is a kind of a magnetic recording/reproducing apparatus, has increased at an annual rate of more than 50% and this tendency is believed to continue into the future. In line with that, a magnetic recording medium suitable for a higher recording density has been developed.
The magnetic recording medium installed in the presently available magnetic recording/reproducing apparatus is a so-called perpendicular magnetic recording medium in which a magnetization easy axis is mainly perpendicularly oriented in a magnetic film. The perpendicular magnetic recording medium is hardly susceptible to a demagnetizing field at a boundary area between recording bits when the perpendicular magnetic recording medium is developed to have a higher recording density, resulting in the realization of a clear formation of a bit boundary. As a result thereof, an increase of noise can be suppressed. Further, as the perpendicular magnetic recording medium is developed to have the higher recording density, a smaller decrease in volume of the recording bit is required. Therefore, the perpendicular magnetic recording medium is resistant to a thermal fluctuation effect. In view of the above, the perpendicular magnetic recording medium has recently attracted a great deal of attention and a medium structure suitable for the perpendicular magnetic recording has been proposed.
To meet with a requirement of realizing the higher recording density of the magnetic recording medium, it has been studied to use a single-pole type head excellent in write-in performance with respect to a perpendicular magnetic layer. In order to work with the single-pole type head, a magnetic recording medium is proposed in which a layer, a so-called backing layer, made of a soft magnetic material is provided between a perpendicular magnetic layer as a recording layer and a non-magnetic substrate, thereby improving the efficiency in input and output of magnetic flux between the single-pole type head and the magnetic recording medium.
However, merely by providing the backing layer in the above-described perpendicular magnetic recording medium, satisfactory results cannot be obtained in recording/reproducing characteristics upon recording and reproducing, thermal fluctuation tolerance, and recording resolution. Therefore, a perpendicular magnetic recording medium excellent in these characteristics is demanded.
More specifically, in order to realize a higher recording density, it is essential to satisfy the demands of both a higher signal-to-noise (S/N) ratio and an improvement of the thermal fluctuation tolerance, wherein the higher S/N ratio refers to make the ratio between a signal and noise upon reproduction greater, and the S/N ratio is an important recording/reproducing characteristic. However, since the two demands above conflict with each other, if one of them is satisfied, the other one becomes unsatisfactory, and thus it is important task to satisfy both demands at a high level.
To solve the above-described problem, proposed is a magnetic recording medium characterized in that 3 magnetic layers are coupled to each other through Anti-Ferro Coupling (AFC) by using a non-magnetic layer and the like, thereby preventing lowering of the S/N ratio while retaining an advantage of lowering the composite Mrt and PW 50 (See, Patent Document 1).
On the other hand, in order to improve the recording/reproducing characteristics and the thermal fluctuation characteristics of the perpendicular magnetic recording medium, proposed is a technique in which an orientation control layer is used to form a multi-layered magnetic layer and a crystal grain of each magnetic layer is formed into a continuous columnar crystal, thereby improving a vertical orientation of the magnetic layers (See, Patent Document 2).
Further, proposed is a technique in which an orientation control layer is formed by a sputtering process using high pressure gas (See, Patent Document 3). Further, in order to further improve the orientation of Ru used as an orientation control layer, proposed is a technique such that the orientation control layer is formed into a double-layered structure, in which an initial layer is formed under low gas pressure and a surface layer is formed under gas pressure higher than the gas pressure used in forming the initial layer (See, Patent Document 4).
It is known that, since a dome-like convex part is formed on a top part of the columnar crystal, the Ru has an effect in a growing crystal grain of the magnetic layer or the like on the convex part and promoting separation of the grown crystal grain to isolate it, thereby growing a magnetic particle into a column shape (See, Patent Document 5).